A torque converter is connected to an engine crankshaft to transmit driving torque to a transmission. There are several methods presently available for connecting the engine and torque converter. One could bolt the converter to the engine through a flexplate, provide radial splines on both an engine mounted flywheel and the torque converter which would be engaged with one another, or use a dogtooth clutch with mating teeth on the engine mounted flywheel and on the torque converter.
Flexplates, radial splines and dogtooth clutches all have their advantages and disadvantages. Flexplates are able to accommodate a slight amount of angular mismatch between the driving axis and the driven axis. Flexplates are difficult to install. It is necessary to bolt the flexplate to the engine crankshaft or to the flywheel after the transmission housing is attached to the engine flywheel housing, requiring extra effort and time for the installation. It also requires that openings be provided in the flywheel housing for access to the attaching fasteners.
Radial splines make transmission installation easier, since the torque converter splines can be slipped into the engine flywheel splines without the need to torque down any bolts. Radial splines are, however, vulnerable to wear, producing increasing amounts of backlash with time. The need for clearance between the mating splines to allow assembly makes the presence of a slight amount of backlash at assembly unavoidable. Backlash results in accelerated wear of the splines and produces undesired noise. This need to produce splines which have a minimum of backlash, yet will go together easily, requires very tight tolerances on the parts. Any slight angular mismatch between the driving member and the driven member will increase the amount of relative motion between the splines, increasing the rate of wear of the splines, and thereby increasing the amount of backlash.
Dogtooth clutches suffer from the disadvantages of the radial splines, and one additional one: they can be difficult to engage. If the teeth are misaligned, engagement will not be possible.